Specimen-positioning systems of the side entry type have found wide application in electron microscopy. In recent years, it has been frequently required that special observations be made using such a specimen-positioning device of the side entry type. One example of special observation is to observe a specimen placed in an atmosphere of a gas. Another example is to observe a moist specimen as it is. In these cases, a specimen chamber having an opening permitting passage of an electron beam is mounted to a holder. The inside of the chamber can be maintained at the atmospheric pressure. A specimen is placed inside the chamber, which is supplied with a given gas or water vapor. Since the specimen holder is required to mount the specimen chamber and a supply pipe, the holder is made large in size. A mechanism for translating and tilting the large specimen holder is also large. As a result, it is inevitable that the whole specimen-positioning device becomes bulky.
When a high-resolution observation is made using a specimen-positioning device of the side entry type, a small-sized system is needed. That is, all of the specimen holder, the translating mechanism, and the tilt mechanism must be small. As the system is reduced in size, the natural frequency of the positioning device increases. Therefore, neither vibration produced inside the electron microscope, for example, due to flow of refrigerant nor extraneous vibration is transmitted to the specimen. Consequently, high-resolution observation is allowed.
High-resolution observation is not achievable with the aforementioned large specimen-positioning device. Conversely, no special observation can be attained with the small specimen-positioning device. Therefore, it has been the common practice to replace the small specimen-positioning device by the large specimen-positioning device when a special observation is made after a high-resolution observation is made employing the small positioning device. Also in the reverse situation, the specimen-positioning device is required to be replaced. This replacement operation involves breaking the vacuum in the microscopic column and disassembling a part of the column. This necessarily prolongs the replacement operation.